There is conventionally known a gantry for a construction machine as disclosed in Patent Literature 1. FIG. 9 shows a gantry 9 equivalent to the aforementioned gantry. The gantry 9 includes a front leg 91, an upper rear leg 92, a lower rear leg 93, and a interconnection section 94. In a working state of the construction machine, the upper rear leg 92 and the lower rear leg 93 extend substantially vertically, and the front leg 91 is inclined obliquely downward and forward. Besides, in a stored state of the construction machine, the lower rear leg 93 and the upper rear leg 92 are lowered while folded, and the front leg 91 is lowered onto the folded upper rear leg 92.
The construction machine includes a slowing frame 90 as a base. The gantry 9 further includes the interconnection section 94 for interconnecting the front leg 91 and the upper rear leg 92 and a connecting rod 95 for connecting the interconnection section 94 to the slewing frame 90 to keep the stored state. The connecting rod 95 includes an upper end portion connected to the interconnection section 94 so as to be a rotation center of the connecting rod 95, and a lower end portion formed with a pin insertion hole 951. The slewing frame 90 is also formed with a pin insertion hole 901, and a pin is inserted into the pin insertion holes 951, 901 to keep the stored state.
With such a construction machine, when a construction work is performed without fixing the lower end portion of the connecting rod 95, the connecting rod 95 possibly swings to collide against the upper rear log 92 and the like, involving damage in paint on the upper rear leg 92 and the connecting rod 95 or occurrence of collision sound. For the reason, the gantry disclosed in Patent Literature 1 includes, as shown in FIG. 9, an engaging pin 96 provided as a shaft portion to the connecting rod 95 and an engagement groove 97 provided as a shaft holding portion at the upper rear leg 92. The engaging pin 96 and the engagement groove 97 are engaged with each other in the working state to prevent the connecting rod 95 from swinging.
Furthermore, with the gantry 9 shown in FIG. 9, upon folding the front leg 91, the upper rear leg 92 and the lower rear leg 93 to enter the stored state, the engaging pin 96 moves from a shaft holding surface 971 of the engagement groove 97 holding the engaging pin 96 over a dislodgement prevention portion 972 located above the shaft holding surface 971 to be dislodged, as shown in FIG. 10. This allows holding of the connecting rod 95 by the shaft holding portion of the upper rear leg 92 to be automatically released.
The conventional gantry described above, however, does not enable the engaging pin 96 of the connecting rod 95 and the engagement groove 97 to be automatically engaged with each other at the time of transition from the stored state to the working state. This requires the engaging pin 96 and the engagement groove 97 to be manually engaged. Such a manual engagement task is burdensome. For example, a worker cannot reach an engagement portion with no step.